My Hoya circular polariser never seems to have that much effect either until I look at the effect on the neg. Unfortunately I cannot compare it to a linear as I have never used one but until you develop and print the neg I wouldn't assume that your circular won't give you the same effect as the linear.

I have never heard of them going "bad" I am not sure what there is in a polariser to stop it working or wear out.

The only thing I would add is that when you get near to having an effect on the sky only a very small movement of the outer glass makes a big difference so it is easy to move it too little or too much at that point